[0001] The present invention relates to controls for determining deployment of passive restraints
in passenger vehicles and more particularly relates to distinguishing different types
and severities of impact events to improve passive restraint deployment decisions.
[0002] For vehicles that include passive restraint systems, it is important to be able to
determine when an impact event is serious enough to warrant deployment of one or more
of these passive restraints in order to protect the vehicle occupants. These may take
the form of front airbags, side airbags, seat belt pretensioners, etc. Likewise it
is also important to determine when an impact event does not warrant deployment to
avoid unnecessary use of the passive restraints, in order to avoid replacement expenses
or risks to the vehicle occupants. Additionally, the deployment decision must be accomplished
a very short time after vehicle impact. This is preferably accomplished while minimising
the expense of the system.
[0003] One current system for determining vehicle impacts involves the use of a single point
acceleration sensor connected to a central processor that evaluates the acceleration
signal. It is more cost effective than other types of impact sensing in that it generally
only requires one sensor, but it must infer the type and severity of impact being
detected in order to accurately and quickly make a deployment decision for the passive
restraints. The manipulation and calculations made with the acceleration signal then,
are key to an accurate deployment decision early in an impact event.
[0004] In many applications of the single accelerometer type of system, then, an approach
is employed where the integral or energy contribution in a velocity change based calculation
is the basis for the actuation decision. Since the energy contribution is largely
determined by the low frequency portion of an acceleration signal, the high frequencies
are filtered out and ignored. This type of strategy, however, while being able to
determine the severity of the impact, will make deployment decision without distinguishing
very well between different types of impacts, which may have different deployment
decisions for different levels of energy involved in the impact, given the short time
frame in which the decision must be made.
[0005] It is thus desirable to be able to employ an accelerometer based impact detection
and passive restraint deployment system with improved accuracy in the deployment decision.
[0006] Also, when one is adapting the particular sensing system for a new vehicle it is
preferable to minimise development time and expense by being able to employ non-destructive
testing to determine the deployment thresholds for various types of vehicle impacts.
[0007] In its embodiments, the present invention contemplates a method of determining passive
restraint deployment for a vehicle having an accelerometer mounted therein comprising
the steps of: generating an acceleration signal from the accelerometer; high pass
filtering the acceleration signal into an impact mode signal in a high frequency range;
low pass filtering the acceleration signal into an impact severity signal in a low
frequency range; comparing the impact mode signal to a predetermined impact mode threshold;
comparing the impact severity signal to a predetermined impact severity threshold;
and sending a deployment signal if both the impact mode threshold and the impact severity
threshold are exceeded.
[0008] The present invention further contemplates a system for determining the deployment
of passive restraints on a vehicle having a single point impact sensor. The system
includes an accelerometer mounted within the vehicle for producing an acceleration
signal, a high pass filter for receiving and filtering the acceleration signal to
produce an impact mode signal, and a low pass filter for receiving and filtering the
acceleration signal to produce an impact severity signal. The system also includes
first means for receiving the impact mode signal and determining the impact mod, second
means for receiving the impact severity signal and determining the impact severity,
and deployment means for making a deployment decision based on the impact mode and
the impact severity.
[0009] An advantage of the present invention is that a more accurate determination can be
made as to passive restraint actuation by taking into account the impact mode and
location when comparing the impact severity determination to a passive restraint actuation
threshold.
[0010] A further advantage of the present invention is that an accurate deployment decision
can be made while maintaining minimum expense and complexity in the sensing and deployment
system.
[0011] Another advantage of the present invention is that the impact sensing system can
be developed for a particular model of vehicle with non-destructive testing, thus
reducing the time and expense needed to adapt the system to a new vehicle.
[0012] The invention will now be described, by way of example, with reference to the accompanying
drawings, in which:
Fig. 1 is a schematic plan view of a vehicle in accordance with the present invention;
Fig. 2 is a schematic view of the electronics of the present invention;
Fig. 3 is a flow chart for the process of the present invention;
Fig. 4 is an example of a high frequency portion of an acceleration signal for a rigid
barrier impact event; and
Fig. 5 is an example of a high frequency portion of an acceleration signal for a centre
pole impact event.
[0013] Fig. 1 illustrates a vehicle 20 including a passenger compartment 22 having front
24 and rear 26 seats therein. Each of the seats includes a seat belt 28. In front
of the front seats 24 are front airbags 30 and adjacent the sides of the front 24
and rear 26 seats are side airbags 32. Also, seat belt pretensioners 34 engage the
seat belts 28. While three different types of passive restraint devices, i.e., front
airbags 30, side airbags 32 and seat belt pretensioners 34, are illustrated herein,
there may only be one or two of these types of passive restraints on a given vehicle.
The present invention is able to be applied to any of these passive restraints.
[0014] Also mounted within the vehicle is a restraints control module 38 and at least one
accelerometer 40. The accelerometer 40 may be a dual axis accelerometer, as is illustrated,
or one or more single axis accelerometers, depending upon the particular passive restraints
employed in the particular vehicle. The dual axis accelerometer 40 includes the capability
to sense longitudinal (fore-aft) acceleration of the vehicle for frontal impact situations
and supply a signal indicating such to the restraints control module 38, and the capability
to sense side-to-side acceleration of the vehicle for side impact situations and supply
a different signal indicating such to the restraints control module 38. In any event,
the accelerometer 40 will supply a signal indicative of the acceleration of the vehicle,
so for purposes of the following discussion, longitudinal acceleration and frontal
impact events will be discussed, although this is equally applicable to side impact
situations.
[0015] Fig. 2 illustrates a schematic diagram of the electronics involved in discrimination
of impact events and passive restraints deployment decisions. The accelerometer 40
is electrically connected to an input port 42 in the restraints control module 38.
The input port 42 connects to a low pass filter 44 and a high pass filter 46 in parallel.
The filters 44 and 46 may be analogue filters, or may be digital filters in which
case an analogue to digital converter will convert the accelerometer signal prior
to entering the filters.
[0016] Both filters 44, 46 are connected to a microcomputer portion 48 of the restraints
control module 38 constituted in a conventional manner, including a central processing
unit 50, read only memory 52, random access memory 54, and an output port 56, all
connected through a common bus. The output port 56 is connected to passive restraints
deployment switches 58, which are in turn connected to the passive restraints, namely,
front airbags 30, side airbags 32, and seat belt pretentioners 34.
[0017] Fig. 3 is a flow chart of the process for determining deployment, illustrating example
signals for the front of a vehicle impacting a fixed barrier. The accelerometer produces
an acceleration signal, block 70. The vertical axis in this block represents measured
acceleration values and the horizontal axis represents time from impact. The acceleration
signal is then decomposed in real time, block 72. This results in a high frequency
signal, block 74, and a low frequency signal, block 76. The high frequency signal
is, for example, above about 100 hertz, and the low frequency signal is, for example,
below about 100 hertz, although this may vary for the particular vehicle in which
the present invention is employed.
[0018] By separating the signal into these two components, manipulation of the original
signal is allowed that will produce more information about the impact itself. The
signal produced by the accelerometer contains two kinds of wave characteristics. The
wave characteristics from the high frequency portion result from an elastic shock
wave emanating from the impact location. By determining the arrival time of this portion
of the signal at the sensor location, in addition to the shape of the wave, one can
determine the mode and location of the impact event. This portion of the signal from
the accelerometer, then, is important, even though it is a poor indicator of the energy
involved with the impact.
[0019] On the other hand, the low frequency portion of the acceleration signal produces
a signal resulting from an inelastic wave. This portion of the signal can be integrated
to produce a velocity change based calculation, indicating the permanent damage to
the vehicle as a result of the energy involved in the impact. This portion of the
acceleration signal, then, will give a very good indication as'to the severity of
the impact event.
[0020] Consequently, as is shown in Fig. 2, the high frequency signal is then interpreted
through an impact mode check, block 78, by comparing features of the high frequency
signal to high frequency features associated with known modes of impact. These modes
may be a pole impact, a rigid barrier impact, an offset impact into a rigid barrier,
a car-to-car impact, etc.
[0021] The low frequency signal is also interpreted, through an impact severity check, block
80, which will determine the amount of energy associated with the impact, regardless
of the mode of the impact. The results of the impact mode check and the impact severity
check are then employed to make a passive restraint deployment decision, block 82.
[0022] The deployment decision will take into account both sets of information. For example,
one way to account for both sets of information is that one determines the impact
mode and uses this to adjust the impact severity threshold. By knowing the impact
mode, then a particular energy threshold for that mode will be compared to the energy
calculated from the impact severity check. If the threshold for that impact mode is
exceeded, then a passive restraint actuation signal will be sent. In this way, different
impact modes will have different thresholds for energy levels, allowing for an improved
actuation decision, while still making the decision in a minimal amount of time. The
information concerning the impact mode and impact severity can also be combined in
other ways, if so desired, to make a deployment decision.
[0023] Figs. 4 and 5 illustrate two examples of high frequency portions of accelerometer
signals for different vehicle impact modes. Fig. 4 is a signal 90 from an eight mile
per hour frontal impact of a passenger car into a rigid barrier, while Fig. 5 is a
signal 92 from a seventeen mile per hour frontal impact of the front-centre of a passenger
car into a pole. One will note the significant differences in the amplitudes of the
high frequency signals. Also, one will note in Fig. 4 the arrival time for the elastic
portion of the signal to reach the sensor location, indicated by an arrowhead 94.
These differences between various impact modes can be identified, even if the low
frequency signal were to indicate similar energy absorption early in the impact event,
thus improving the actuation decision.
[0024] Another advantage of the present invention is that, by employing these particular
separate signals for deployment decisions, non-destructive testing is possible for
adapting the system to a new model of vehicle, while still maintaining good accuracy
in the deployment decisions.
[0025] For the high frequency, elastic shock wave portion of the acceleration signal, the
sensor system can be calibrated for a particular model of vehicle by a non-destructive
hammer test. This is done by impacting a vehicle at a given location with a bunt object
and measuring the time for the wave to reach the sensor as well as the amplitudes
of the initial pulse. One can then calibrate the software in the control module to
recognise the signal for that location. The blunt object impact can be small enough
to avoid permanent damage to the impact location. Further, the low frequency thresholds
may be determined with computer aided engineering impact simulations on computer models
of the particular model of vehicle to estimate energy levels. Computer simulation
can be used since only impact severity needs to be determined and not greater details
as to the character of the signal, since this is accomplished by the high frequency
signal.
1. A system for determining the deployment of passive restraints on a vehicle having
a single point impact sensor comprising:
an accelerometer (40) mounted within the vehicle for producing an acceleration signal;
a high pass filter (46) for receiving and filtering the acceleration signal to produce
an impact mode signal;
a low pass filter (44) for receiving and filtering the acceleration signal to produce
an impact severity signal;
first means (78) for receiving the impact mode signal and determining the impact mode;
second means (80) for receiving the impact severity signal and determining the impact
severity; and
deployment means (82) for making a deployment decision based on the impact mode and
the impact severity.
2. A method of determining passive restraint deployment for a vehicle having an accelerometer
mounted therein comprising the steps of:
generating an acceleration signal from the accelerometer;
high pass filtering the acceleration signal into an impact mode signal in a high frequency
range;
low pass filtering the acceleration signal into an impact severity signal in a low
frequency range;
comparing the impact mode signal to a predetermined impact mode threshold;
comparing the impact severity signal to a predetermined impact severity threshold;
and
sending a deployment signal if both the impact mode threshold and the impact severity
threshold are exceeded.
3. A method as claimed in claim 2, wherein the high frequency range is generally above
100 hertz.
4. A method as claimed in claim 3, wherein the low frequency range is generally below
100 hertz.
5. A method as claimed in claim 2, wherein the low frequency range is generally below
100 hertz.
6. A method as claimed in claim 2, further including the step of determining a type of
impact from the impact mode signal, prior to the step of comparing the impact mode
signal to a predetermined impact mode threshold.
7. A method as claimed in claim 6, further including the step of determining a location
of impact on the vehicle from the impact mode signal, prior to the step of comparing
the impact mode signal to a predetermined impact mode threshold.
8. A method as claimed in claim 2, further including the step of determining a location
of impact on the vehicle from the impact mode signal, prior to the step of comparing
the impact mode signal to a predetermined impact mode threshold.
9. A method as claimed in claim 2, wherein the step of comparing the impact severity
signal includes integrating the impact severity signal over a predetermined time interval
to produce a velocity change signal, and comparing the velocity change signal to the
predetermined impact severity threshold.
10. A method of determining passive restraint deployment for a vehicle having an accelerometer
mounted therein comprising the steps of:
generating an acceleration signal from the accelerometer;
high pass filtering the acceleration signal into an impact mode signal in a high frequency
range;
low pass filtering the acceleration signal into an impact severity signal in a low
frequency range;
creating a predetermined impact severity threshold;
adjusting the impact severity threshold based upon the impact mode signal;
comparing the impact severity signal to the adjusted impact severity threshold; and
sending a deployment signal if the impact severity signal exceeds the adjusted impact
severity threshold.